Boundary layer control



Oct. 10, 1967 H. PAPST BOUNDARY LAYER CONTROL Original Filed Dec. 23, 196 3 3 Sheets-Sheet 1 Fig.3

Fig.1

17B Fig.5

In venlor: Hermann Papst his ATTORNEY Oct. 10, 1967 H. PAPST 3,346,235

BOUNDARY LAYER CONTROL Original Filed Dec. 23, 1963 3 Sheets-Sheet? In ven tor.-

Hermann Papst W a 437w his A TTORNEY Oct 1967 H. PAPST 3,346,235

BOUNDARY LAYER CONTROL Original Filed Dec. 23, 1963 3 Sheets-Sheet 5 Fig.1! Fig.12 41a 41c 17' 51 g-' 18 15 1s Fig.14

Inventor:

Hermann Papst BY may; f nzwhis A TTURNEY United States Patent 3,346,235 BOUNDARY LAYER CONTROL Hermann Papst, St. Georgen, Black Forest, Germany Original application Dec. 23, 1963, Ser. No. 332,619. Divided and this application Mar. 16, 1966, Ser. No. 534,889 Claims priority, application Germany, Dec. 24, 1962, P 30,859 6 Claims. (Cl. 253-39.15)

The present application is a division of my copending application Serial No. 332,619, filed December 23, 1963, and entitled Boundary Layer Control Means and Method of Producing the Same, now abandoned.

The present invention relates to profiled bodies which come in direct contact with fluid streams, and more particularly to improvements in means for controlling the boundary layer which develops along the outer surfaces of such profiled bodies. Specifically, the invention relates to boundary layer control means which is suitable for use in blowers, and many other types of machines wherein at least some component parts come in direct contact with fluid streams.

The problems which arise as a result of the fact that a thin layer of air or water will develop along the exposed surfaces of blades, vanes and similar profiled bodies are Well known to designers of vehicles, blowers and turbines. Attempts to utilize porous skins have met with little success because the pores will become clogged after comparatively short periods of exposure to a fluid stream and because such pores reduce the smoothness of the skin so that the fluid stream meets greater resistance even if the boundary layer is eliminated. Also, a porous skin is weaker than a nonperrneable skin.

Accordingly, it is an important object of the present invention to provide a novel skin construction which is configurated in such a way that it eliminates at least some strata of the boundary layer which develops along the exposed surfaces of blades, vanes, shells and similar profiled bodies which come in direct contact with fluid streams.

A further object of the invention is to provide a profiled body whose skin is constructed and mounted in such a way that it prevents the formation of boundary layers and that it may simultaneously perform at least one additional function, such as to cool the profiled body, or to reduce the pressure in the interior of a profiled body.

An additional object of my invention is to provide a profiled body which is provided with improved boundary layer control means of the above outlined characteristics and wherein the provision of such boundary layer control means adds little to the initial cost of the profiled body.

A concomitant object of the instant invention is to provide improved boundary layer control means which does not appreciably affect the strength of the profiled body, which may be manufactured and finished in conventional machines, and which may eliminate the boundary layer on all or on selected surface portions of a profiled body.

Still a more specific object of the invention is to provide an improved outer covering or skin for vanes, blades, shells and similar profiled bodies, and to construct the covering in such a way that it permits entry of boundary layer into the interior of the profiled body but is not likely to be clogged by solid or liquid impurities which are contained in the fluid stream.

A further object of the invention is to provide an outer covering which need not consist of porous material and which need not be slotted or apertured in order to eliminate at least some strata of the boundary layer from a member or body provided with such covering.

Another object of the invention is to provide a wing, blade or vane, which embodies the boundary layer control means of the present invention.

A further object of the invention is to provide a fluid displacing machine, such as a pump, compressor, blower or turbine, which embodies the boundary layer control means of my invention.

With the above objects in view, one feature of my invention resides in the provision of an outer covering or skin which, when applied to a blade, vane, wing, or a similar profiled body, will serve as a highly effective boundary layer control means to remove at least some strata of the boundary layer and to thus reduce the resistance which the profiled body meets in moving with reference to a surrounding fluid stream or vice versa. One side of the sheet is formed with depressions whose width preferably decreases in a direction from the one side to the other side of the sheet and these depressions are open on both sides so that the sheet is formed with slots whose width increases in a direction from the other toward the one side of the sheet. When a body of the type in question is constructed by placing a sheet of such skin material around a skeleton frame of an airfoil in such a way that the narrower ends of the slots are located at the outer side of the thus obtained outer covering or skin, any foreign matter which will eventually penetrate into the slots cannot remain therein because the width of the slots increases inwardly. Also, each slot is preferably bounded by inclined faces which diverge inwardly, i.e., in a direction from the exposed side toward the concealed side of the skin so that, and if the pressure in the interior of the body is less than the pressure of the surrounding fluid, the boundary layer is actually sucked into the body and undergoes minimal deflection (substantially less than degrees) while flowing through the slots. The slots are preferably but need not always be perpendicular to the direction of fluid flow, and they may be staggered with reference to each other so as to insure that the boundary layer may be removed from all sections of the outer surface.

The sharp edges of the skin at both sides of each slot will actually peel the boundary layer and will compel it to penetrate through the slots and into the interior of a profiled body in which the skin is used as an outer covering.

If the outer side of the skin is coated with one or more layers of lacquer, paint or the like, such materials cannot clog the slots because the width of the slots essentially increases in a direction from the inner side to the outer side of the skin.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved boundary layer control means itself, however, both as to its construction and the method of producing the same, together with additional features and advantages thereof, will be best understood from the following detailed description of certain specific embodiments with reference to the accompanying drawings, in which:

, FIG. 1 is a vertical section through a ram constituting one shaping die of an embossing apparatus for the production of skins which embody the boundary layer control means of the present invention;

FIG. 2 is a section through a matrix which constitutes another shaping die of the embossing apparatus;

FIG. 3 is a vertical section through the embossing apparatus showing the ram in idle position and further show ing a portion of a skin which is deformed by the working ends of embossing tools on the ram;

FIG. 4 is a fragmentary side elevational view of a finished skin;

FIG. 5 illustrates a portion of a modified embossing apparatus with the matrix partly broken away;

FIG. 6 illustrates a third embossing apparatus wherein the ram carries a roller-shaped embossing tool;

FIG. 7 is a front elevational view of a milling machine which is utilized for removing ridges from a skin;

FIG. 8 is a side elevational view of a polishing machine which is used for precision finishing of the skin after the skin has been treated by the milling machine of FIG.

FIG. 9 is a transverse section through an embodiment which comprises a skin of the type shown in FIG. 8;

FIG. 10 is a fragmentary axial section through a radial blower whose blades are provided with skins embodying my invention;

FIG. 11 is a fragmentary axial section through an axial blower whose blades and vanes are constructed in a manner as shown in FIG. 9;

FIG. 12 is a fragmentary front elevational view of an impeller whose blades resemble the body of FIG. 9;

FIG. 13 is a section through a turbine blade which is provided with a skin of the type shown in FIG. 4;

FIG. 14 is a fragmentary front elevational view of a modified blade;

FIG. 15 is a section through a different turbine blade.

To facilitate understanding of the invention I have shown in FIGS. 13 and 5-8 various devices which may be used in making my boundary layer control means, whereas the remaining figures illustrate the outer covering or skin itself and various applications to which it may be put.

Referring to FIGS. 1 to 3, there is shown an embossing apparatus which comprises a set of shaping dies including a matrix 2 whose upper side is provided with elongated grooves 3, and a ram 1a having a plurality of embossing tool 1 detachably secured thereto by a series of bolts 1b so that the precision-finished, smooth-surfaced, wedge-shaped elongated working ends 10 of the tools I register with the grooves 3. The ram 10 is reciprocable toward and away from the matrix 2, or vice versa, whereby the working ends 10 deform a skin 9 which is placed onto the upper side of the matrix so as to overlie the grooves 3. This skin is a sheet of aluminum alloy and the working ends 16 impress in the upper side thereof a series of staggered but parallel depressions 6 of triangular cross section whereby the underside of the sheet is provided with complementary ridges 12. The height of the working ends 1c exceeds slightly the thickness of the skin 9 so that the depth of each depression 6 also exceeds the thickness of the skin. The depressions 6 are bounded by smooth inclined faces 7 which diverge in a direction from the underside toward the upper side of the skin 9. The ridges 12 are removed by a suitable milling, polishing, grinding or planing machine (two embodiments of such machines will be described in connection with FIGS. 7 and 8) whereby the skin is formed with narrow slots 10, see FIG. 4, whose width increases in a direction from the underside toward the upper side of the sheet material. The ridges 12 are removed in such a way that the underside of the skin 9 is smooth and that it merely shows the narrower ends of the slots 10. The upper side of the skin is provided with the depressions 6 whose longitudinal ends are preferably rounded in a manner shown in FIG. 4, and such roundness is due to the configuration of grooves 3 in the upper side of the matrix 2.

If the slots 10 are comparatively long, at least some of the working ends 1c may be provided with channels 5 extending transversely of the edges 4 so that the material of the skin 9 forms a series of webs 8, shown in FIG. 4, which divide the respective slot into a series of aligned sections 10a. The webs 8 improve the resistance of the skin to bending or twisting stresses and such webs are of particular advantage when the slots are comparatively long, when the slots are closely adjacent to each other, and/ or when the material of the skin 9 is readily deformable. The slots are staggered in such a way that they extend along the full length or width of the skin 9, depending on the position of the skin on a profiled body which is placed into a fluid stream. For example, and if the skin of FIG. 4 forms the outer covering of a wing, the wing moves in a direction from the left to the right, or vice versa, so that the slots 10, 10a extend substantially transversely of the fluid stream and at least some strata of the boundary layer developing along the side of the skin which is exposed to the fluid stream will flow continuously and with minimal deflection first through the slots and thereupon along the other side of the skin. In actual use, the outer side of the skin is that side from which the inclined faces 7 diverge outwardly, i.e., in FIG. 3 the outer side is the underside of the skin 9, and FIG. 4 shows the inner side of this skin. The inclined faces 7 direct the strata of the boundary layer during their flow through the slots 10, 10a and insure that the boundary layer must be deflected through an angle of substantially less than degrees. This reduces turbulence in the interior of the profiled body.

When the working ends 10 penetrate into the upper side of the skin 9, and when the embossing apparatus is closed, the skin is held flat between the underside of the ram 1a and the upper side of the matrix 2 so that the surfaces of the skin remain smooth and that the working ends 10 merely shift certain layers of the material of the skin. The height and the inclination of surfaces on the working ends 1c will determine the width of the slots 10, i.e., the same embossing apparatus may be used for forming different slots merely by exchanging the embossing tools. The lower part of the ram 1a carries a series of spacer elements 1g which enable the operator to change the distance between the embossing tools 1 so that the ram may be used with different matrices. All such features contribute to greater versatility of the embossing apparatus.

The working ends 16 will not sever or rip through the material of the skin but merely cause plastic deformation of its material. Since the faces of the working ends 10 are smooth, they cannot produce fissures or similar defects in the skin, especially since the upper side of the matrix is preferably finished with great precision. The slots 10, 10a are not likely to become clogged by paint, lacquer, rain, dust, sleet or snow because they diverge inwardly so that any matter which has penetrated through the narrow outer ends of the slots is free to enter the interior of the profiled body which is surrounded by the skin. This is of particular importance in road vehicles and in watercraft wherein the outer covering is exposed to dust, mud or water, and such configuration of the slots is of equal importance when the outer covering is coated with paint, lacquer or the like.

FIG. 5 illustrates a modified embossing apparatus which is especially suited for shaping of large skins. The apparatus comprises one, two or more reciprocable rams 1A which are guided by one or more arms 11 and which cooperate with one or more fixed matrices 2A. The arms 11 are slidable along vertical ways 11a mounted on a frame 11b, and this frame comprises an overhanging head which accommodates a hydraulic or pneumatic reciprocating mechanism 11d for the rams 1A. The matrices 2A and the rams 1A may be located in inclined planes, depending on the configuration and dimensions of the skins to be treated.

If desired, the fluid-operated reciprocating means 11d may be replaced by a simple lifting mechanism which serves to move the rams 1A away from the matrices 2A whereupon the rams are released to descend by gravity and to thereby deform a sheet overlies the matrices. However, it is normally advisable to provide hydraulic or pneumatic reciprocating means which cause the rams to descend at high speed and to strike against a skin with a force sufficient to produce the ridges 12 in a single operation. It is also possible to deform the skin by pressure waves produced by impulse generators or explosions while the skin is imersed in a fluid medium.

FIG. 6 illustrates a third embossing apparatus wherein the matric 2B cooperates with a ram 1B which carries one or more roller-shaped embossing tools 21. The skin 9 is placed onto the upper side of the matrix 28 and the tool 21 is caused to move in the longitudinal direction of the groove 33 (see the double-headed arrow 21a) while the ram 1B exerts a pressure in a direction toward the matrix (arrow 21b). The tool 21 may be moved back and forth only once or more than once, depending on the thickness and rigidity of the skin 9.

Referring to FIG. 7, there is shown a portable milling machine 25 having a rotary milling cutter 25a which serves to remove the ridges 12. The cutter 25a travels between pair-wise arranged guide rollers 26 and its housing 25b comprises two handles 27 which may be grasped by hand to move the milling machine in the longitudinal direciton of the ridges 12. One of the handles 27 accommodates or carries a motor (not shown) which drives a shaft 25c serving to rotate the cutter 2511 through a gear train 25d. The skin 9 forms the outer covering of an airfoil and is applied to the skelton frame 9a of the airfoil in such a way that the ridges 12 extend beyond the outer side thereof, i.e., beyond that side which is exposed to the fluid when the airfoil moves with respect to a fluid stream or vice versa. The edges of the milling cutter 25a remove all such material which extends beyond the outer side of the undeformed (nonembossed) portion of the skin 9 whereby the skin is provided with narrow slots 10 which are substantially parallel with the leading and trailing edges of the airfoil. Each slot 10 diverges in a direction from the outer side toward the inner side of the skin 9 and each such slot is bounded by two smooth inclined faces 7. An important advantage of the just described mode of assembling and finishing the airfoil of FIG. 7 is that removal of the ridges 12 takes place simultaneously with thorough and precise finishing of the exposed side of the skin 9. Since such precision finishing is normally needed irrespective of the provision of boundary layer control means, removing the ridges 12 does not consume any additional time because it is incidental to precisiontreatment of the skin. The rollers 26 prevent penetration of the cutter 2511 into the nondeformed portions of the skin, and FIG. 7 shows that the lower panel 9' of the skin 9 is already free of ridges 12 so that it merely exhibits a series of suitably distributed slots 10.

If the skin must be finished with utmost precision, one can resort to a grinding or polishing machine 30, for example of the type which is shown in FIG. 8. This machine may be used in addition to or as a substitute for the milling machine 25 and comprises an endless grinding or polishing belt 30b which is trained around rollers 30a, 32, 32a to travel across the slots 10. One of these rollers is driven in a manner not forming part of my invention, and the belt 30b is tensioned by a fourth roller 30c which is mounted on a spring-biased arm 30d. The frame 302 of the machine 30 carries an arcuate deflector 31 which is adjustable and which bears against the inner side of the belt 30b. The curvature of the deflector 31 corresponds to the curvature of an upper panel 9" forming part of a skin 9 which surrounds the skeleton frame. When the machine 30 polishes the lower panel 9' of the skin 9, the operator replaces the deflector 31 by a differently configurated deflector. Alternatively, the deflector '31 may consist of elastically deformable material so that it follows the outline of the panel 9 or 9".

The skeleton frame comprises a transversely extending corrugated frame member 13 whose sections 14 extend between the panels 9, 9". The member 13 forms an annular stiffener whose inner and outer sides are respectively surrounded by tubular skins 9', 9".

Finishing of the body of FIG. 7 or 8 may be carried out as follows: First, the embossed skin 9 is stretched onto and is connected with the skeleton frame 9a or 13 so that its ridges 12 extend outwardly. These ridges are then removed by the milling cutter 25a and, finally, the outer side of the skin is precision-finished by the belt 30b. If the material of the belt can remove the ridges 12 without previous milling, the machine 25 may be dispensed with.

It goes without saying that the ridges 12 may be removed by many other types of existing milling, grinding or planing machines, and that such ridges may be removed before the skin is mounted on a skeleton frame. For example, one may utilize automatic milling machines with copying means or a large skin may be treated simultaneously by two or more automatic, semiautomatic or portable machines.

The length of slots 10 should be selected in such a way that the edges bounding each slot remain parallel to each other even if the skin 9 is deformed, for example, at the time it is applied around the skeleton frame of an airfoil, chassis, cowling, fuselage or the like. As a rule, the Width of the slots 10 need not substantially exceed one millimeter and may be a small fraction (one or more tenths) of a millimeter.

It is normally preferred to remove the ridges 12 subsequent to deformation of the skin 9, especially if the skin consists of thin and readily deformable sheet material, because the likelihood that the slots 10 would be of unequal width is more pronounced if the slots are formed prior to deformation (shaping) of the skin. It is also conceivable to form the slots 10 by grinding or by erosion with spark discharge, but such methods are costlier than the embossing method.

To contribute to a better understanding of the invention, and to illustrate at least partially the variety of uses to which the novel method may be placed, FIGS. 9-15 show various applications on hand of specific examples. Having thus described, by way of example and to facilitate better understanding of the invention, how the skin or covering may be produced, I will now proceed to describe various different embodiments of the invention.

FIG. 9 illustrates in a section an airfoil, e.g., a blade in a turbine or blower whose outer covering consists of a skin 9 which is provided with boundary layer control means embodying my invention. The skin comprises a lower panel 9 and an upper panel 9" both surrounding an apertured skeleton frame 13. The panels are provided with elongated knife blade-like edge portions 15 which extend along the trailing edge of the airfoil and which are held apart by spacer elements 16 so that the edges 15 define between themselves a series of orifice 17. Such orifices are of advantage irrespective of the exact configuration of slots 10 in the panels 9, 9" as long as the skin 9 allows at least some strata of the boundary layer B (shown in broken lines) to enter the interior of the airfoil. When the airfoil is caused to move with reference to the fluid stream or vice versa, there develops a low-pressure zone immediately downstream of the orifices 17 so that the orifices actually suck fluid from the interior of the airfoil to draw the boundary layer through the slots 10. The flow of the fluid stream is indicated by arrows 17a and the flow of the boundary layer B through the slots 10 is indicated by arrows 1717. Thus, the provision of orifices 17 results in increased flow of the boundary layer into and through the slots 10 so that the edges 15 actually form a suction nozzle which draws the boundary layer into the airfoil and which thereupon injects the thus accumulated body of fluid into the low-pressure zone along the trailing edge of the airfoil. In other words, the nozzle will cause deflection of the boundary layer so that at least some strata of this layer will penetrate through the slots 10 which extend transversely of the fluid stream.

FIG. 10 illustrates a portion of a radial blower 35 which comprises a series of hollow radially arranged blades 27. One axial end of each blade 37 is welded to a disk 30 whose flange 30a is secured to the rotor 36a of an electric motor 36. The other axial end 39 of each blade 37 is soldered to a hollow annulus 40 which rotates with the rotor 36a whereby the channels between the blades 37 receive streams of fluid from the suction side of the blower and such streams flow in directions indicated by the arrows 35a. The blades 37 are constructed in a manner as illustrated in FIG. 9 so that the inner strata of the boundary layer may enter through the slots 10 and are expelled through orifices defined by the nozzles at the outer ends of the blades. The pressure in the channels between the blades 37 exceeds the pressure in the interior of the blades so that the boundary layer is compelled to enter the blades whereby the streams of fluid meet less resistance in flowing toward the pressure side of the blower with resultant increase in the efliciency and operating range of the blower. The slots 10 are substantially parallel to the axis of the rotor 3611.

FIG. 11 shows a portion of a multistage axial blower whose motor 42 includes a rotor 42a supporting a ring of moving blades 43 each constructed in a manner as illustrated in FIG. 9, i.e., each blade defines at least one orifice 17 located at the pressure side of the ring. The blades 43 cooperate with a ring of stationary vanes 41 which are also constructed in a manner as described in connection with FIG. 9 and which are located at the suction side of the blower. The vanes 41 are carried by a tubular support 41a which defines a duct 41b and comprises ports 41c through which fluid entering the slots 10 of the vanes 41 may be led away. The main streams of fluid flow in directions indicated by the arrows 43a. Such strata of the boundary layer which enter through the slots 10 of the blades 43 are evacuated through the orifices 17 and flow toward the pressure side of the blower. The blades 43 are further provided with orifices 17' at the outer ends thereof so that a least some fluid of the boundary layer will escape by centrifugal force when the motor 42 is in operation. The support 41a carries additional rings of stationary vanes (not shown) which discharge fluid into the duct 41b.

FIG. 12 illustrates a portion of an impeller wheel 44 which is provided with arcuate blades 45. These blades are constructed in a manner as illustrated in FIG. 9, and each thereof has at its outer end an orifice 17. When the wheel 44 rotates, the fluid which enters through the slots 10 of the blades 45 is expelled through the orifices 17 to in crease the efllciency of the apparatus in which the impeller wheel is in use.

Referring to FIG. 13, there is shown a portion of a blade which is installed in a gas turbine, especially in a gas turbine which is used in connection with exceptionally hot fluids. The front portion of the blade defines a compartment 46 for a suitable coolant which is discharged through one or more openings 47 provided in the leading edge of the blade. There is a deflector 47a, located in front of the openings 47, to direct thin streams of coolant along the outer sides of the panels 9', 9 so that such streams separate the hot fluid (arrows 46a) from the panels, For example, the coolant which enters the compartment 46 may be air, water vapor, nitrogen, carbon dioxide or another nonoxidizing gas. The compartment 46 receives coolant through one or more nozzles 48 which dis charge the coolant at high pressure so that a layer of such coolant will be caused to flow from the openings 47 along the outer sides of the panels 9, 9" without causing any turbulence. The pressure of coolant entering at 48 must exceed the pressure of the fluid stream which opposes the outflow of coolant through the openings 47. It will be noted that the front portion of the skin 9 which surrounds the compartment 46 is not slotted.

The deflector 47a shields the coolant issuing from the openings 47 so that such coolant cannot meet the fluid stream head on and is automatically deflected to flow along the outer sides of the panels 9, 9". It was found that such coolant will form a coat at least along the upper panel 9" when the turbine is in actual use.

As the layers of coolant continue to flow along the outer sides of the panels 9', 9", they are sucked through the slots 10 and enter the rear compartment 49 of the blade to be expelled through the orifices at the trailing end in the same way as described in connection with FIG. 9. Thus, the layers of coolant form a protective coat which prevents direct contact between the stream of hot fluid and the material of the skin 9. The skin 9 of FIG. 13 preferably consists of a nickel or chrome alloy and is treated in a manner as described in connection with FIGS. 1 to 8.

FIG. 14 shows the outer end portion of a hollow turbine blade wherein the leading edge is parallel with the trailing edge. The blade comprises a skin 9 which is formed with staggered slots 10, and the panels of this skin form at the trailing edge a series of suction orifices 17. The edges 15, 16 of these panels are provided with spacer elements in the form of lugs 18 which are formed by removing the material at the inner sides of such edges to that each orifice extends between a pair of adjacent lugs 18. Each lug 18 of one panel is welded to the other panel, preferably by an impulse welding process and in such a way that all lugs are welded in a single operation. Such mode of welding insures that any melting of the skin is restricted to immediate vicnity of the lugs. The blade of FIG. 14 is equally useful in aircraft, e.g., it may form the wing of an airplane.

FIG. 15 illustrates a portion of an airfoil, such as a blade in a turbine, a radial blower or the like. This blade comprises a forged skeleton profile 50 one side of which is provided with cutouts or grooves 51 extending toward the root of the blade. The cross-sectional area of each cutout increases gradually in a direction toward the tip of the blade so that the blade can withstand substantial centrifugal forces and considerable bending or twisting stresses. The cutouts 51 are covered by a skin 9 having slots 10 which communicate with the cutouts so that the boundary layer may penetrate into the cutouts when the blade of FIG. 15 rotates. If desired, the profile 50 may be provided with additional cutouts at the underside thereof and the skin 9 then surrounds both sides of the profile. The skin preferably consists of high-quality metallic material and is welded to the profile 50. The outer end of each cutout 51 is open and communicates with the surrounding atmosphere so that the material of the boundary layer is free to escape when the blade rotates. It was found that the blade of FIG. 15 will not vibrate when it is used in a turbine or a similar fluid displacing machine.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a fluid-displacing machine, a plurality of hollow blades rotatable about a fixed axis and each having two curved opposed Walls, a leading side wall and a trailing side Wall means, and end wall means provided at one end of the blade, said curved opposed walls each having an outer and an inner side and at least one of said curved walls being provided With a plurality of narrow slots extending transversely of the direction of movement of the fluid streams and tapering in width from said inner to said outer side, said slots having at said outer side a constant cross-section and being bounded by mutually inclined opposite faces extending between said inner and said outer side; and fluid outlet means diverging in the direction of fluid flow and provided in said trailing side wall means communicating with the interior of the respective blade so that fluid entering such blades through said slots may escape by centrifugal force when said blades rotate.

2. A structure as defined in claim 1, wherein said fluid outlet means is additionally provided in said end wall means.

3. A structure as defined in claim 1, wherein said fluid outlet means is spaced farther from said fixed axis than said slots are spaced from the latter.

4. A structure as defined in claim 1, wherein each of said opposite faces defines with said outer side an angle of up to but not including 90 degrees.

5. A structure as defined in claim 6, said blades each being provided in the respective leading side walls thereof with aperture means; and further comprising cooling means communicating with the interior of the respective blades and introducing a cooling fluid thereinto at a pressure exceeding the pressure of the fluid stream acting on said leading side wall, so that said cooling fluid passes outwardly through said aperture means and is distributed over the blade by the pressure of said fluid stream.

6. In a fluid-displacing machine a plurality of hollow blades rotatable about a fixed axis and each having two curved opposed walls, a leading side Wall and a trailing side wall means, and end wall means provided at one end of the blade to said curved opposed walls, each having an outer and an inner side and at least one of said curved walls being provided with a plurality of narrow slots extending transversely of the direction of movement of the fluid stream and tapering in width from said inner side to said outer side, said slots having at said outer side a constant cross-section and being bounded by mutually inclined opposite faces extending between said inner and said outer side; fluid outlet means provided in one of said wall means communicating with the interior of the respective blade so that fluid entering such blade through said slots may escape by centrifugal force when said blades rotate; and inner support means arranged in the respective hollow blades in contact with said curved walls and provided with channel means extending to said fluid outlet means and widening in the direction toward the same, said slots communicating with said channel means.

References Cited UNITED STATES PATENTS 2,406,920 9/ 1946 Stalker 230-122 2,501,614 3/1950 Price 230122 2,817,490 12/ 1957 Brotfitt 283-77 2,847,185 8/1958 Petrie et a1. 25339.1 3,032,314 5/ 1962 David 25 3-77 FOREIGN PATENTS 945,397 11/1948 France. 1,021,265 11/ 1952 France.

12,794 1910 Great Britain. 404,817 1/1934 Great Britain. 73 0,147 5/1955 Great Britain. 754,055 8/ 1956 Great Britain.

DONLEY J. STOCKING, Primary Examiner.

HENRY F. RADUAZO, ROBERT M. WALKER,

Examiners. 

1. IN A FLUID-DISPLACING MACHINE, A PLURALITY OF HOLLOW BLADES ROTATABLE ABOUT A FIXED AXIS AND EACH HAVING TWO CURVED OPPOSED WALLS, A LEADING SIDE WALL AND A TRAILING SIDE WALL MEANS, AND END WALL MEANS PROVIDED AT ONE END OF THE BLADE, SAID CURVED OPPOSED WALLS EACH HAVING AN OUTER AND AN INNER SIDE AND AT LEAST ONE OF SAID CURVED WALLS BEING PROVIDED WITH A PLURALITY OF NARROW SLOTS EXTENDING TRANSVERSELY OF THE DIRECTION OF MOVEMENT OF THE FLUID STREAMS AND TAPERING IN WIDTH FROM SAID INNER TO SAID OUTER SIDE, SAID SLOTS HAVING AT SAID OUTER SIDE A CONSTANT CROSS-SECTION AND BEING BOUNDED BY MUTUALLY INCLINED OPPOSITE FACES EXTENDING BETWEEN SAID INNER AND SAID OUTER SIDE; AND FLUID OUTLET MEANS DIVERGING IN THE DIRECTION OF FLUID FLOW AND PROVIDED IN SAID TRAILING SIDE WALL MEANS COMMUNICATING WITH INTERIOR OF THE RESPECTIVE BLADE SO THAT FLUID ENTERING SUCH BLADES THROUGH SAID SLOTS MAY ESCAPE BY CENTRIFUGAL FORCE WHEN SAID BLADES ROTATE. 